A major concern of this article is to document the role of paraprofessionals in providing services for clients in the mental health and psychiatric fields. There are basically three types of paraprofessionals. The first type is the "old" hospital worker; he does not have a college degree, is not indigenous to the community in which he is working, comes from a low income background, is frequently Black or Puerto Rican, and does supportive therapeutic work. The second is typically a woman with a degree, generally engaged in substantive therapeutic work, and, mainly, white. The third is the indigenous paraprofessional who does hold a degree, is generally employed, and is engaged in therapeutically relevant work. A wide range of data on these professionals was collected. Although no one of the studies conducted is conclusive by itself, a number of them such as the Ellsworth study are well controlled and offer powerful evidence. However, the multiplicity of evidence derived from a great variety of different sources, stemming from different investigator biases, using diverse methods and indices, leads to the conclusion that paraprofessionals play an important role as treatment agents and contribute to the improved mental health of clients and patients in highly significant, often unique ways. (Author/CK)